In a large mixing bowl, combine the yeast and water until dissolved. Add the cake mix, vanilla, salt and flour. Mix well - the dough will be slightly sticky.

Cover the bowl tightly with plastic wrap. Let rise for one hour. Punch down the dough and allow to rise again for another 45 minutes.

On a lightly floured surface, roll the dough into a large rectangle about ¼-inch thick. Spread the lemon curd all over the dough evenly. Sprinkle the brown sugar over the lemon curd.

Roll up like a jellyroll, starting on the long edge. Slice into 24 equal pieces.

Grease two 9x13-inch baking pans. Arrange the sweet roll slices in the pans. Cover and let rise in a warm place until doubled in size.

Preheat oven to 350°F.

Bake for 15-20 minutes or until cooked through.

While the sweet rolls are baking, prepare the icing by mixing the butter, powdered sugar, vanilla and 4 tbsp. milk in a medium mixing bowl until creamy. Add more milk, only if necessary, until desired consistency is reached.

Top sweet rolls with icing. Top with sprinkles, if desired. Serve.